Partially hydrolyzed aluminum alkyl compounds known as aluminoxanes (AO) are used for activating transition metals for olefin polymerization activity. One such compound, methylaluminoxane (MAO), is a frequently chosen aluminum co-catalyst/activator in the industry. Considerable effort has been devoted to improving the effectiveness of catalyst systems based on use of aluminoxanes, hydroxyaluminoxanes, or modified aluminoxanes for polymerization of olefins. Representative patents and publications in the field of aluminoxane usage include the following: U.S. Pat. No. 5,324,800 to Welborn et al.; U.S. Pat. No. 4,752,597 to Turner; U.S. Pat. Nos. 4,960,878 and 5,041,584 to Crapo et al.; WO 96102580 to Dall'occo, et al.; EP 0 277 003 and EP 0 277 004 to Turner; Hlatky, Turner, and Eckman, J. Am. Chem. Soc., 1989, 111, 2728-2729; Hlatky and Upton, Macromolecules, 1996, 29, 8019-8020. U.S. Pat. No. 5,153,157 to Hlatky and Turner; U.S. Pat. No. 5,198,401 to Turner, Hlatky, and Eckman; Brintzinger, et al., Angew. Chem. Int. Ed. Engl., 1995, 34, 1143-1170; and the like. Hydroxyaluminoxane compositions are disclosed in U.S. Pat. Nos. 6,562,991, 6,555,494, 6,492,292, 6,462,212, and 6,160,145. Despite technological advances, many aluminoxane-based polymerization catalyst activators still lack the activity and/or thermal stability needed for commercial applicability, require commercially unacceptably high aluminum loading, are expensive (especially MAO), and have other impediments to commercial implementation.
U.S. Pat. No. 5,384,299 describes zwitterionic catalyst systems prepared by protolysis from dialkyl-metallocenes and borate anions. WO 91/09882 describes supported cationic metallocene catalysts based on the above-mentioned borate anion, wherein the catalyst system is formed by application of a dialkyl-metallocene compound and a Bronsted-acid, quaternary ammonium compound having a non coordinating anion, tetrakispentafluoroborate, to an inorganic support. The support is modified beforehand by means of a trialkylaluminum compound. One disadvantage of this method of application to a support is that only a small part of the metallocene used is immobilized by physisorbtion on the support material; and, thus, the metallocene is prone to detach from the support surface, which can ultimately lead to reactor fouling.
WO 96/04319 describes a catalyst system in which the borate activator anion is covalently bound to the support material directly through one oxygen atom of the metal oxide support. However, such a catalyst system has a low polymerization activity by commercial standards. Another disadvantage of such a catalyst system is described by Basset et al. (J. Am. Chem. Soc., 128 (2006) 9361). Basset et al. describe catalyst deactivation pathways for such covalently bound (through one oxygen atom of the metal oxide, silica, support) borate activator anions as well as a deactivation pathway involving the reaction of the four member siloxane rings of the silica support (formed by calcination of the silica up to and greater than 600° C.). Deactivation pathways described in publications show the limitations of borate activator anions covalently bound to one oxygen atom of the metal oxide carrier and additionally, the importance of controlling the structures within the metal oxide carrier as a result of calcination.
Thus, there is a need for activator compositions that are stable to deactivation pathways and that exhibit high sustainable activity for commercial olefin polymerizations.